A capacity of a radio link between a transmitter and a receiver can be increased by applying a so-called MIMO-, SIMO- or MISO transmission (MIMO=Multiple Input Multiple Output, SIMO=Single Input Multiple Output, MISO=Multiple Input Single Output). Single input means, that only one antenna element is applied for transmitting radio frequency signals from the transmitter. Multiple input means, that two or more antenna elements form a transmit antenna array for transmitting the radio frequency signals from the transmitter. Single output means, that one antenna element is applied for receiving the radio frequency signals at the receiver. Multiple output means, that two or more antenna elements form a receive antenna array for receiving the radio frequency signals at the receiver.
Radio frequency signals are usually linearly polarized and a polarization direction corresponds to an electrical field vector of the radio frequency signals. The electrical field vector is always orthogonally aligned to a propagation direction of the radio frequency signals. The transmit antenna array and the receive antenna array are usually not aligned to each other, especially when the transmitter and/or the receiver are movable. Furthermore, a transmission path of the radio frequency signals from the transmit antenna array to the receive antenna array is not always identical to a shortest route between the transmit antenna array to the receive antenna array due to reflections and scattering. Therefore, the polarization direction of the received radio frequency signals may not correspond optimally and may not be parallel aligned to polarization directions of excitation areas of antenna elements of the receive antenna array.